Fluid pressure actuated diaphragm switch



Sept. 2, 1969 L. REICHERT E AL FLUID PRESSURE ACTUATED DIAPHRAGM SWITCHFiled Oct. 9. 1967 & xwmx INVENTORS Ludwig REICHERT Werner HEINLEINUnited States Patent 3,465,112 FLUID PRESSURE ACTUATED DIAPHRAGM SWITCHLudwig Reichert, Waiblingen, and Werner Heinlein, Stuttgart, Germany,assignors to Robert Bosch GmbH, Stuttgart, Germany Filed Oct. 9, 1967,Ser. No. 673,604 Claims priority, application ggrmany, Aug. 23, 1967,

9, Int. Cl. Hlllh 35/40 US. Cl. 20083 9 Claims ABSTRACT OF THEDISCLOSURE A fluid pressure actuated switch whose housing is providedwith an internal annular recess for the marginal portion of anelastomeric semielastic diaphragm.whose central portion bulges into thepressure chamber, of the housing. The pressure chamber is locatedopposite a second chamber which receives one or more contacts. When thepressure chamber receives a fluid, thecentral mrtion of the diaphragmtends to flatten out with resultant radial expansion of the diaphragm.This radial expansion is resisted by contact of the diaphragm edge withthe bottom wall of the recess so that the material of the marginalportion of the diaphragm yields in axial direction, whereby thethickness of the marginal portion increases so that the latter alsobears against the side walls of the recess to provide a fluidproof sealbetween the two chambers. Prior to admission of fluid into the pressurechamber, the thickness of the marginal portion at most equals the axiallength of the recess.

BACKGROUND OF THE INVENTION The present invention relates toimprovements in fluid pressure actuated diaphragm switches.

German Patent No. 1,080,189 discloses a diaphragm switch whose housingaccommodates a diaphragm having a marginal portion tightly clamped by asteel ring so that it undergoes axial compression. The diaphragm dividesthe interior of the housing into a pressure chamber and a second chamberwhich accommodates one or more electric switch contacts. The centralportion of the diaphragm bulges into the pressure chamber and isdeformed in response to admission of pressurized fluid to actuate theswitch. The steel ring cooperates with an internal shoulder of thehousing to clamp the marginal portion of the diaphragm.

A serious drawback of such pressure responsive switches is that theirparts must be machined and assembled with a high degree of precisionwhich contributes to high initial cost and result in a large number ofrejects. The clamping action of the aforementioned ring must be selectedwith a view to prevent damage to the marginal portion of the diaphragm.The interior of the housing must be machined with a high degree ofprecision to insure satisfactory bulging of the diaphragm and to avoidunevennesses on the aforementioned shoulder because the unevennessescould result in damage to the marginal portion of the diaphragm.

SUMMARY OF THE INVENTION It is an important object of the presentinvention to provide a simple, compact, inexpensive and rugged fluidpressure actuated diaphragm switch.

Another object of the invention is to provide a diaphragm switch whichcan operate properly even if its component parts are not machined orotherwise finished with a high degree of precision.

A further object of the invention is to provide a diaphragm switchwherein the marginal portion of the diaphragm need not be clamped in thehousing but the diaphragm is still capable of preventing escape of fluidfrom the pressure chamber.

An additional object of our invention is to provide a diaphragm switchwherein the diaphragm may be installed in the housing in a novel andtime-saving way.

Briefly outlined, our invention is embodied in a fluid pressure actuatedelectric switch which comprises a housing having an internal surfaceprovided with an annular recess of predetermined axial length or width,a deformable diaphragm inserted into the housing and having a marginalportion received in the recess whereby the interior of the housing isdivided into a pressure chamber and a second chamber or switch contactchamber, the marginal portion of the diaphragm having a thickness whichis less than or at most equals the width of the recess and the diaphragmfurther having a central portion which bulges into the pressure chamber,and a nipple or analogous means for admitting into the pressure chambera gaseous or liquid pressure fluid to stress the diaphragm withresulting thickening of the marginal portion whereby the latter providesa fluid-tight seal between the two chambers. The central portion of thediaphragm flattens out in response to admission of fluid into thepressure chamber so that the diaphragm tends to expand radially withensuing thickening of the marginal portion. 7

The housing is preferably provided with an apertured partition locatedin the second chamber to constitute a back support for the centralportion during admission of fluid into the pressure chamber. Thepartition can slidably guide a trip in the form of a plug or rivet whichcauses opening or closing of the switch in response to admission offluid into the pressure chamber. The trip is preferably biased againstthe central portion of the diaphragm by a suitable spring installed inthe second chamber.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved switch itself, however, both as to its construction and itsmode of operation, together with additional features and advantagesthereof, will be best understood upon perusal of the following detaileddescription of certain specific embodiments with reference to theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partly elevational andpartly axial sectional view of a fluid pressure actuated diaphragmswitch which embodies one form of our invention, the diaphragm beingshown in unstressed condition;

FIG. 2 is a similar view of the switch but showing the diaphragm instressed condition;

FIG. 3 is an axial sectional view of the diaphragm as it appears priorto insertion into the housing of the switch;

FIG. 4 is an axial sectional view of a second diaphragm;

FIG. 5 is an axial sectional view of a third diaphragm; and

FIG. 6 is a fragmentary axial sectional view of a housing which formspart of a modified switch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The fluid pressure actuateddiaphragm switch of FIG. 1 comprises a metallic housing or casing 1having a lower portion 2 surrounding a pressure chamber or plenumchamber 3 for a pressurized fluid which can be admitted through an inlethere shown as a nipple 4 which is integral with the housing 1. Thedischarge end of the central bore 5 in the inlet 4 is adjacent to thebulging central portion 8a of a disk-shaped diaphragm 8 whose marginalportion 8b extends into an annular recess or groove 7 provided in theinternal surface of the housing 1. The lower axial end of the recess 7is bounded by an annular shoulder 6 of the housing 1. The marginalportion 8b of the diaphragm 8 has a cylindrical peripheral surface 8'which is illustrated in FIG. 3, the latter showing the diaphragm as itappears prior to insertion into the housing 1. The diaphragm consists ofoil-resistant elastic material, preferably rubber or synthetic plastic,and is produced by injection molding. The diameter of the recess 7 issmaller than the diameter of the peripheral surface 8' in unstressedcondition of the diaphragm.

The upper axial end of the recess 7 is bounded by a radially outwardlyextending shoulder 9 of the housing 1 which serves as a seat for adisk-shaped partition 10 constituting a back support for the centralportion 8a of the diaphragm 8 when the latter is stressed in response toadmission of a gaseous or liquid fluid through the bore of the inlet 4.The partition is received in a second annular recess 11 of the housing 1which is adjacent to and whose diameter is larger than that of therecess 7. The axial length or width of the recess 7 (between theshoulders 6 and 9) is slightly greater than the thickness of themarginal portion 8b of the diaphragm 8. For example, the width of therecess 7 may exceed the thickness of the marginal portion 8b by one ormore tenths of a millimeter, preferably no more than one millimeter.Since the diameter of the peripheral surface 8' exceeds the diameter ofthe recess 7, the diaphragm 8 is deformed in response to insertion intothe housing 1 and its central portion 8a bulges away from the partition10, i.e., into the pressure chamber 3. In other words, the material ofthe marginal portion 8b of the diaphragm 8 is forced from all sidestoward the center of the diaphragm. The space between the downwardlybulging central portion 8a and the underside of the partition 10 (asviewed in FIG. 1) accommodates the head 14 of a reciprocable rivetshapedtrip 13 whose stem 15 extends through a central aperture 16 of thepartition and whose disk-shaped upper end 14a extends into a secondchamber 17 of the housing 1. The head 14 bears against the concave sideof the central portion 8a of the diaphragm 8 and the disk-shaped upperend 14:: is biased downwardly by a helical return spring 14baccommodated in the chamber 17. The end portion 14a can complete anelectric circuit between two electric contacts 17a, 17b in the secondchamber 17 or it can move these contacts upwardly to thereby open orclose the switch. The numeral 12 denotes an annular bead which overliesthe upper side of the partition 10 and is formed by upsetting a portionof the housing 1 above the second recess 11. This bead 12 holds thepartition 10 in the illustrated position and permanently locks thediaphragm 8 in the space below the partition.

FIG. 1 illustrates the switch in inoperative position, i.e., when thediaphragm 8 is unstressed because the bore '5 of the inlet 4 is sealedor disconnected from a source of pressurized fluid. If the bore 5 admitsfluid, the central portion 8a of the diaphragm 8 is stressed andundergoes deformation in a manner as shown in FIG. 2. The bulge of thecentral portion 8a is reduced and a larger part of this central portionbears against the underside of the partition 10. Of course, thethickness of the marginal portion 8b of the diaphragm 8 increases inresponse to flattening of the central portion 8a whereby the marginalportion completely fills the recess 7 and provides a fluidtight sealbetween the chambers 3 and 17. In other words, the thickness of themarginal portion 8b of the diaphragm 8 then equals the axial distancebetween the shoulders 6 and 9, and such thickening takes place inresponse to relatively small flattening of the central portion 8a. Themarginal portion 8b is then tightly clamped between the shoulder 6 andpartition 10, and such clamping or sealing action improves in responseto increasing fluid pressure in the chamber 3, namely, in response toprogressing flattening of the central portion 8a. It was found duringactual testing that the diaphragm 8 can readily withstand extremely highpressures in the range of atmospheres above atmospheric pressure withoutany leakage of fluid into the chamber 17. When the diaphragm 8 isstressed in a manner as shown in FIG. 2, the central portion 8adisplaces the trip 13 whereby the upper end portion 14a of the tripengages the contacts 17a, 17b and thus actuates the switch, for example,by moving the contacts upwardly. The stem 15 is guided in the aperture16 so that it prevents tilting of the trip 13. If the pressure of fluidin the chamber 3 drops, the diaphragm 8 reassumes its unstressed ornormal condition and its central portion 8a again assumes the shapeshown in FIG. 1. In the absence of the spring 14b, the trip 13 movesdownwardly by gravity and is disengaged from the contacts 17a, 17b. Ifthe contacts 17a, 17b are movable with reference to the housing 1, theyalso return to their normal positions as soon as the fluid pressure uponthe diaphragm 8 is relaxed sufficiently to permit more pronouncedbulging of the central portion 80.

FIG. 4 illustrates in section a second diaphragm 18 whose centralportion 19 bulges prior to insertion into the housing 1. The diameter ofthis diaphragm 18 need not exceed the diameter of the recess 7. Thebulge of the central portion 19 can be produced in a number of ways, forexample, during injection molding or by deformation in response tolocalized heating. The thickness of the marginal portion 18a of thediaphragm 18 is less than or at most equals the width of the recess 7.The thickness of this marginal portion 18a may but need not be the sameas the thickness of the central portion 19. When the diaphragm 18 isinserted into the housing of a pressure actuated switch, the centralportion 19 :bulges into the pressure chamber, i.e., toward the inlet.When the inlet admits a pressurized fluid, the stressing of diaphragm 18takes place in the same way as described in connection with FIG. 2 andthe marginal portion 18a becomes thicker to provide a reliable sealbetween the pressure chamber and the second chamber. It is clear thatthe diameter of the diaphragm 18 may exceed the diameter of the recess 7so that the diaphragm undergoes at least some deformation and the bulgeof its central portion 19 increases in response to insertion into theswitch housing. This also insures that the diaphragm seals the pressurechamber from the second chamber at all times, i.e., also when the inletis disconnected from a source of pressurized fluid so that the fluidpressure in pressure chamber is the same as that in the second chamber.

It is also possible to employ a disk-shaped diaphragm which isabsolutely or substantially flat prior to insertion into the switchhousing and consists of semielastic material. On prolonged stay in thehousing, the semielastic diaphragm retains the :bulge of its centralportion even if it is removed from the housing. Thus, when a semielasticdiaphragm is removed from the housing after a certain period of time, itresembles the diaphragm 18 of FIG. 4 even though it was originally aflat disk similar to the one shown in FIG. 3.

FIG. 5 illustrates a further diaphragm 20 which also resembles a flatdisk and has a conical peripheral surface 20' composed of two conicalportions which taper away from the respective axial ends. An advantageof the diaphragm 20 is that its marginal portion 20a can move into verysatisfactory sealing engagement with the cylindrical or conical portionof the internal surface of a housing which surrounds the recess 7 or asimilar recess. The two conical parts of the marginal portion 20a canprovide a very satisfactory sealing action prior to admission of a fluidinto the pressure chamber and they allow for more rapid radial and axialdeformation of the marginal portion 20a in response to admission offluid into the pressure chamber. In other words, the trip 13 or ananalogous actuating device can operate the switch in response to arelatively small rise in fluid pressure in the pressure chamber. It wasfound that the diaphragm 20 of FIG. 5 is also very effective when thepressure chamber accommodates a fluid medium, i.e., that its sealingaction is satisfactory not 'only in unstressed but also in stressedcondition of the central portion.

Referring finally to FIG. 6, there is shown a modified switch housing 21wherein the recess 22 is bounded by a conical portion of the internalsurface of the housing. This recess 22 tapers away from the bore 5' ofthe inlet 4'. The partition is installed in a second recess in the sameway as described in connection with FIG. 1. The diaphragm has beenomitted for the sake of clarity, The conicity or taper of the recess 22can be achieved by exerting upon the shoulder 9' of the housing 21 anaxial pressure which reduces the diameter of the upper end of the recess22. This recess can accommodate any one of the diaphragms -8, 18 and 20and the conical surface portion bounding the recess 22 insures a verysatisfactorysealing action in unstressed and/ or stressed condition ofthe diaphragm. The deformation or thickening of the marginal portionwill begin in response to a relatively small fluid pressure, and thesealing action improves with increasing fluid pressure. The shoulder 23corresponds to the. shoulder 6 of FIG. 1 and the numeral 17' denotes acontactcontaining chamber at the upper side of the partition 10.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of our contribution to the art and, therefore, suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. In a fluid pressure actuated switch, a combination comprising ahousing having an internal surface provided with an annular recess ofpredetermined axial length and bounded by two axially spaced side facesand an annular bottom face having a predetermined diameter; a diaphragmconsisting of elastomeric material, having a predetermined thickness anda predetermined diameter greater than the diameter of said annularbottom face, said diaphragm being inserted into said housing and havinga circumferentially extended marginal portion received in said recesswhereby the interior of said housing is divided into a pressure chamberand a second chamber, the thickness of said marginal portion beingslightly smaller than said predetermined axial length of said recess andsaid diaphragm when inserted having a central portion bulging into saidpressure chamber due to said predetermined diameter of said diaphragmwhich is greater than said predetermined diameter of said annular bottomface of said recess; and means for admitting into said pressure chambera pressure fluid to compress said diaphragm with resulting radiallyoutwardly directed pressure on said diaphragm whereby, due to resistanceto such pressure by said annular bottom face of said recess, thematerial of said marginal portion is displaced in axial direction withconcomitant thickening of said marginal portion whereby said marginalportion tightly engages said side faces of said recess and provides afluid-tight sea between said chambers.

2. A switch as defined in claim 1, wherein said diaphragm has a diameterwhich approximates the diameter of said recess and said control portiondefines an at least slightly pronounced bulge prior to insertion of saiddiaphragm into said housing.

3. A switch as defined in claim 1, wherein said dia phragm consists ofoil-resistant material.

4. A switch as defined in claim 1, wherein said marginal portion of thediaphragm has a cylindrical peripheral surface.

5. A switch as defined in claim 1, wherein said marginal portion of thediaphragm has a conical peripheral surface.

6. A switch as defined in claim 1, wherein said recess tapers in adirection from one of said chambers toward the other chamber.

7. A switch as defined in claim 6, wherein the taper of said recess isdue to deformation of a portion of said housing.

8. A switch as defined in claim 1, wherein said diaphragm is a flat diskwhose diameter exceeds the diameter of said recess before said marginalportion is received in said recess.

9. A switch as defined in claim 1, said diaphragm having prior toinsertion thereof into said housing a diameter which at least equals thediameter of said annular recess.

References Cited UNITED STATES PATENTS 2, 694,415 11/ 1954 Dillon.2,284,424 5/ 1942 Hein 277-177 2,741,678 4/1956 Schaefer et a1. ZOO-83.93,093,716 6/ 1963 Horowitz 20083 3,218,051 11/1965 Doetsch 277-177 XBERNARD A. GILHEANY, Primary Examiner H. B. GlLSON, Assistant Examiner.

US. Cl. X.R. 337-306

